As a method for obtaining a compound having hydroxyl groups by reducing an ester compound, for example, the following methods have been proposed.
(1) A method of reducing a compound of the following formula (I) to a compound of the following formula (II) by using a reaction mixture containing ethanol, sodium borohydride and an organic base (potassium tert-butoxide, sodium ethoxide or the like) (Patent Document 1):ROC(═O)—CFW1—O—Rf—CFW2—C(═O)OR  (I)HOCH2—CFW1—O—Rf—CFW2—CH2OH  (II)wherein R is a C1-5 alkyl group, W1 and W2 are a fluorine atom or a trifluoromethyl group, and Rf is a perfluoroplyoxyalkylene group.
(2) A method of reducing 3-phenylpropionmethyl by using sodium borohydride and a metal salt in tetrahydropyran (Patent Document 2).
However, when the present inventors tried the method of (1), compounds of which all terminal ends are reduced could not be efficiently obtained due to the weak reducing force. Further, in a case where the method of (1) was applied to compounds having at least three —C(═O)OR, a problem was observed that reduction reaction intermediates agglomerated in the reduction reaction, and the reaction thereby stopped halfway.
In a case where the method of (2) is applied to perfluoro group-containing compounds having —C(═O)OR, there are problems such that since the solubility of the perfluoro group-containing compounds is low in tetrahydropyran, a heterogeneous reaction results, or time is required to accomplish the reaction.
Further, when the method of (2) was applied to perfluoro group-containing compounds having at least 2 —C(═O)OR, a problem was observed such that reduction reaction intermediates agglomerated in the reduction reaction, and the reaction stopped halfway.